Calcining furnace and method of operating the same



E. KLOHN March 18, 19.30.

CALCINING FURNACE AND METHOD. OPERATING THE SAME Filed Aug. 3. 1921Patented Man 18;

UNITED STA TES PATENT OFFICE ERNST KIbHN', O1 BEBLIN-WILMERSDORF,GERMANY, ASSIGNOR TO THE FIRM ZAHN & 60., G. M. B. 11., OF BERLIN,GERMANY CALCIN'ING FURNACE AND METHOD OF OPERATING THE SAME Applicationfled August a, 1927, Serial m5.

My invention relates to improvements in calcining furnaces and themethod of operating the same.

In the circular calcining furnaces with stationary hearths, hithertoknown, the parts which are most sensitive to attack by heat andchemicals, namely the central pedestal with the arm cross and securingdevices for the arms, are located within the heated furnace. These partstherefore had to be made of expensive acid and fireproof steel andexchanging of the stirrer arms during operation was practicallyimpossible, despite proposals for convenient exchanging; for after ashort period of operation the exchangeable members were attacked andchanged, so that the exchange could only be effected when the furnacewas allowed to get cold, when the securing devices could be convenientlyreached.

According to the present invention the centre of the calcining furnace,wherein the devices for securing and moving the stirrer arms arelocated, is surrounded by masonry and thereby separated from the heatedcalcining space. Within the separated part therefore are located thecentre shaft with the arm cross, and the devices for securing thestirrer arms to the arm cross. The stirrer arms move in a slot in themasonry surrounding the centre, which slot is packed in such a mannerthat, for example acid vapours cannot reach the shaft on thecentrepedestal. The latter can therefore be of simple machinery cast iron.

The secure operation of the furnace according to the invention isfurther guaranteed by the feature that at the point at which the feedingarrangement is provided, heating from below does not take place, thusensuring that the hearth plates are not so rapidly attacked by thefreshly introduced and at first most strongly reacting chemicals.

Further the heating in the neighbourhood of the feed point is notsostrong in that the gases proceeding directly from the fire andtherefore are there hottest reach the material being calcined only atthe end of its path through the annular furnace shortly before it isremoved. The particular form taken 210,350, and in Germany December 30,-1926.

by the annular furnace according to the invention therefore permits thecounter current principle to be employed, which has hitherto only beenproposed in long extended sulphate furnaces, but which has not yet beenused in circular furnaces.

The furnace according to the present invention is particularly adaptedfor the manufacture of sulphate from salt and sulphuric acid or salt andbisulphate, but can also be used for other calcining processes.

The accompanying drawing shows by way of example an embodiment offurnace in accordance with the present invention. Figure 1 shows thefurnace in vertical section and Figures 2 and 3 show sections on thelines 2-2 and 33 of Figure 1.

The annular muifle furnace is indicated by l and the unheated circularinner space by 2. The fire gases which come from the heating place 19pass first in the direction of'the arrow into the upper heating channel3, then pass through the passage 4 into the lower fire channel 5traversing the latter-in the same direction and after having thus passedtwice round the annular mufile furnace leave through the passage 6. Thefeeding of the furnace takes place through an opening 7 the removal ofthe calcined materials through the outlet opening 8. As appears from,Fig. 3, the brickwork below the opening 7 is solid, the fire channel 5ending at opposite sides of the said opening and away therefrom.

The inner circumferential wall of the furnace surrounding the chamber 2is formed with a continuous circumferential slot 15, and in order tosupport the top part of the brickwork an annular plate 20 is providedwhich is suspended by means of bars 21 from beams 22 disposed above 'thefurnace. To prevent the escape of gases from the calcining chambersuitable packing means are provided. As shown the said packing means arein the form of upper and lower rings 16 made from channel irons andfixed to the inner wall of the brickwork, the said rings being engagedby rings 17 fixed to the arm-cross and formed at their top with acircumferential channel 23 engaged by the downwardly directed flange ofthe upper channel iron. The lower ring 16 and the ring 23 are filledwith sand or other packing medium. In order to prevent bending of thearm-cross due to the weight of the stirrer arms, it is provided withdownwardly directed arms 18 carrying rollers 24 supported on an annulartrack 25.

I claim:

1. A circular muffle calcining furnace, comprising an annular hearthhaving an inner circumferential wall formed with a continuouscircumferential slot, heating means for said hearth, stirrer armsprojecting through said annular slot from the median part of the furnaceinto the hearth, a ring carried by said stirrer arms in position forcovering sai slot, packing members fixed to said circumferential walland cooperating with said ring for closing said slot, and means forrotating said stirrer arms.

2. A circular mufile calcining furnace, comprising a stationary hearthhaving bottom and top walls, annular heating channels located above andbelow said hearth, the inner circumferential wall of said hearth beingformed with a circumferential slot, stirrer arms projecting from themedian part of the furnace through said slot and into said hearth, meansfor rotating said stirrer arms, means for successively passing heatinggas through said heating chambers, and a feeding passage extendingdownwardly into said hearth, he portion of the bottom wall of the hearthbelow said feeding passage being made solid, and the connection betweenthe upper fire passage and the lower fire passage being made by apassage which when looking in the direction of the flow of the heatinggas is located behind said feeding passage. 3. A method of operatingcircular 'muflle calcining furnaces providedwith rotary stirrer arms, inwhich the fire gases first traverse three quarters of the furnacethrough the upper fire passage, until they reach the freshly introducedmaterials and then again pass round the furnace through the lowerfirepassage before they leave the furnace, while the stirring device movesthe material to be calcined in a direction counter to that of the firegases.

4. A circular mufiie calcining furnace, comprising an annular hearthhaving an inner circumferential wall formed with a continuouscircumferential slot smaller in height than the hearth, heating meansfor said hearth, stirrer arms projecting through said annular slot fromthe median part of the furnace into the hearth, the said median partcircumscribed by said circumferential wall having a diameter sufficientto permit access to said stirrer arms, and means for rotating saidstirrer arms.

5. A circular muffle calcining furnace, comprising an annular hearthhaving an inner uous circumferential slot, heating means for saidhearth, stirrer arms projecting through said annular slot from themedian part of t e furnace into the hearth, means for rotatin saidstirrer arms, and means movable wit said stirrer arms for closing saidslot.

6. A circular muflle calcining furnace, comprising a stationary annularhearth having bottom and top walls, annular heating channels locatedabove and below said hearth, stirrer arms projecting into said hearth,means for passing heating gas through said heating channels, and achargin passage extending downwardly into said earth, the heatingchannel below said hearth ending at opd posite sides of said chargingpassage and away therefrom thus providing a solid bottom between itsends below said charging passage.

In testimony whereof I hereunto affix my signature.

ERNST HDHN.

circumferential wall formed with a contin-

